Processes for the mining of sulfur by the Frasch method have been known for many years. The process which was developed about 1890 by Herman Frasch, provides a process for recovering sulfur from subterranean deposits by heating vast quantities of water to about 320.degree. F. and pumping this water down wells into the sulfur formation. The heated water fuses the sulfur in the formation such that the sulfur can be lifted to the surface in the liquid state by conventional methods, such as with an air lift. Several United States patents were obtained by Frasch on this process, including U.S. Pat. Nos. 461,429, 461,430, 799,642, 800,127, 870,620, 928,036, 977,444, 988,995, 1,008,319, and 1,152,499.
The Frasch process primarily concerns the recovery of sulfur from a pristine field from which up to about 70% of the total reserves can be recovered. Once the primary recovery is competed, however, there remains substantial quantities of sulfur in the formation. There has been substantial published prior art seeking ways to recover the additional sulfur. For example, the prior art has used combinations of a sulfur well with a bleed well in attempts to recover additional sulfur. Disclosures of this type of system may be found in U.S. Pat. Nos. 1,615,050, 1,615,051, 1,719,981, 1,764,538, 2,991,987, and 3,041,274. The bleed well, however, is simply used in this system to discharge or recover water from the sulfur formation.
Later work in this area includes U.S. Pat. No. 2,109,611, a 1938 patent, which reuses mine bleed water in a process for sulfur recovery. However, there is no disclosure in the patent for treatment of the water to recover sulfur. U.S. Pat. No. 2,771,284, a 1956 patent, removes sulfur deposits from sulfur mining pipes using a hot caustic soda solution. U.S. Pat. No. 2,917,345, a 1959 patent, is directed to a method for producing a sulfur slurry for transportation of solid sulfur. In this patent the process includes mixing molten sulfur produced by the Frasch process with cold water in a dispersing or grinding machine to produce a slurry. U. S. Pat. No. 3,578,418, a 1971 patent, is directed to a solvent extraction process for recovering sulfur from ores. U.S. Pat. No. 3,718,366, a 1973 patent, is directed to a method for creating permeability in sulfur deposits by underground fusion mining of sulfur using a modified Frasch process. According to this process, the rate of production of molten sulfur is increased by increasing the permeability of the sulfurcontaining formation by creating a fracture between the producing well and the bleed well using an explosive. However, this patent does not recover sulfur from the bleed well.
U.S. Pat. No. 4,241,953, a 1980 patent, discloses methods for reuse of sulfur mine bleed water wherein the underground water is brought to the surface, mixed with fresh heated water and returned underground to met the subterranean sulfur using a return pipeline which is separate and distinct from the pipeline through which the molten sulfur is brought to the surface.
The present invention provides a sulfur recovery system wherein primary, secondary and tertiary sulfur recovery is made possible to greatly increase the amount of sulfur that can be obtained from the formation.